Electronic smoke apparatus such as electronic cigarettes provide a smoking alternative to smokers. An electronic smoke is a non-naked flame smoking apparatus which typically comprises a battery powered heater arranged to vaporize liquid nicotine or nicotine substitutes upon actuation by a user. The heater is usually automatically actuated by a controller when a user inhales through the electronic smoke to simulate a smoking action. Typically, an inhaling detector is provided in an electronic smoke and the controller, such as a digital signal processor (DSP) will actuate the heater when inhaling is detected by the inhaling detector. An exemplary equivalent application circuit of a conventional electronic cigarette is shown in FIG. 1.
The inhaling detector of a conventional electronic smoke apparatus typically comprises an air-flow sensor having a structure similar to that of a conventional microphone condenser of FIG. 2. A typical air-flow sensor of a conventional electronic smoke comprises a variable capacitor (Cs) comprising a membrane and a back plate, a pre-charged electret layer (Vs), and a junction field effect transistor (JFET) arranged as schematically shown in FIG. 2. The DSP of the smoking circuitry is arranged to actuate the heater automatically when vibration, which is assumed to be due to inhaling, is detected by the air-flow sensor. However, such an arrangement is not very reliable since false actuations are common, especially in a noisy environment. Furthermore, the structure of a conventional air-flow sensor is relatively complicated and more expensive, since a JFET stage is required to amplify signals detected by the vibrating membrane and an electret layer is in combination with a back plate to form a reference capacitive surface.
Therefore, it would be advantageous if an improved air-flow sensor for an electronic smoke could be provided.
In this specification, the terms electronic smoke and electronic smoke apparatus are equivalent and includes electronic smoke apparatus which are commonly known as electronic cigarettes, electronic cigar, e-cigarette, personal vaporizers etc., without loss of generality.